Core orientation is the process of obtaining and marking the orientation of a core sample from a drilling operation.
The orientation of the sample is determined with regard to its original position in a body of material, such as rock or ore deposits underground.
Core orientation is recorded during drilling, and analysis is undertaken during core logging. The core logging process requires the use of systems to measure the angles of the geological features, such as an integrated core logging system.
Whilst depth and azimuth are used as important indicators of core position, they are generally inadequate on their own to determine the original position and attitude of subsurface geological features. Core orientation i.e. which side of the core was facing the bottom (or top) of a borehole and rotational orientation compared to surrounding material, enables such details to be determined.
Through core orientation, it is possible to understand the geology of a subsurface region and from that make strategic decisions on future mining or drilling operations, such as economic feasibility, predicted ore body volume, and layout planning.
In the construction industry, core orientation can reveal geological features that may affect siting or structural foundations for buildings. Core samples are cylindrical in shape, typically around 3 meters long, and are obtained by drilling with an annular hollow core drill into subsurface material, such as sediment and rock, and recovering the core sample.
A diamond tipped drill bit is used at the end of the hollow drill string. As the drill progresses deeper, more sections of hollow steel drill tube are added to extend the drill string. An inner tube assembly captures the core sample. This inner tube assembly remains stationary while the outer tubes rotate with the drill bit. Thus, the core sample is pushed into the inner tube.
A ‘back end’ assembly connects to a greaser. This greaser lubricates the back end assembly which rotates with the outer casing while the greaser remains stationary with the inner tubing.
Once a core sample is cut, the inner tube assembly is recovered by winching to the surface. After removal of the back end assembly from the inner tube assembly, the core sample is recovered and catalogued for analysis.
Various core orientation systems have previously been used or proposed. Traditional systems use a spear and clay impression arrangement where a spear is thrown down the drill string and makes an impression in clay material at an upper end of the core sample. This impression can be used to vindicate the orientation of the core at the time and position the spear impacted the clay.
A more recent system of determining core orientation is proposed in Australian patent number 2006100113 (also as U.S. Pat. No. 7,584,055). This patent document describes a core orientation device for a core drill. The device provides signals associated with a physical orientation of a core orientation device for a particular moment in time. The device includes a memory for storing and providing the orientation data when required.
The system described in AU 2006100113 provides a two unit replacement for the greaser described above. A first orientation system unit houses electronics and a battery used to record orientation data, and the second greaser unit is an extended greaser accommodating a physical screw on connector for the first unit as well as serving as the greaser. This combination forms part of the inner tube assembly with the core tube, orientation system ‘first’ unit and the connector/greaser ‘second’ unit.
However, as a result of the now extended length of the combined orientation system and greaser units compared with a standard greaser only unit, the outer drill string casing now requires a matching extension piece to extend the outer casing an equal amount. The core orientation system has a display on one face which is used when setting up the unit prior to deployment, and to indicate core sample alignment when the core sample is recovered. At the surface before removing the core sample from the inner tube assembly, the operator views the display fitted on the system. The display indicates for the operator to rotate the unit and the sample within the tube until the whole core tube and sample is oriented with the lower section of the core sample at the lower end of the tube. The core sample is marked (usually by pencil) before being removed from the core for future analysis.
However, the device described in AU 2006100113 has been found to have certain limitations. The orientation unit is connected to the greaser by a screw thread and o-ring seal arrangement. In the harsh down hole environment within the drill string, it has been realised that the o-ring seals are not always effective and can let fluid into the space between the orientation unit and the greaser. The display unit allows fluid into the electronics of the orientation, resulting in a risk of fault or failure of the device. Furthermore, the orientation unit must be disassembled from the greaser unit before the display and orientation unit can be viewed, rotated and the required core orientation displayed. Thus, the device of AU 2006100113 requires manual manipulation before any reading can be viewed on the display, if the display and the electronics have survived any ingress of fluid past the o-ring seal.
Similar issues arise with downhole probes that are used to obtain borehole telemetry data to determine drilling progress, such as depth and direction of the borehole and change in surrounding magnetic field.
Typically the downhole equipment is brought to the surface once sufficient data is gathered or task completed, such as obtaining a core sample. It is common practice to manually have to separate the backend assembly from an electronics package used for gathering downhole data. This task involves unscrewing the backend assembly from the electronics package, which takes time and risks thread damage as well as resulting in risk of ingress of dirt and water into the thread. Also, o-ring seals protecting the electronics unit may be compromised through separation and refitting of the backend assembly and electronics unit. Similar issues exist with separating the electronics unit of a downhole probe from its backend assembly.
It has been found desirable to provide means of obtaining signals/data from or providing signals/data to downhole equipment electronics units, such as used in core sample orientation units or downhole probes.
One improved system is described in the applicant's international patent application PCT/AU2011/000954, the contents of which are incorporated herein in its entirety. At least one embodiment described in PCT/AU2011/000954 utilises an optical device extending from an end of a data gathering device, such as an electronics unit, into an end of a greaser unit. Light from LEDs in the data gathering device is reflected out of apertures in the greaser unit behind the optical device. The present invention improves on such a system.
With this in mind, it has been found desirable to provide improved means for obtaining signals/data from or providing signals/data to an electronics unit of downhole equipment.